1. Field of the Invention
The present invention relates to an automatic sheet feeding apparatus for stacked sheets separating from one another and feeding them one by one, and a recording apparatus having the automatic sheet feeding apparatus.
2. Description of the Related Art
A recording apparatus for forming images on sheets, such as a printer, copying machine or facsimile, or a reading apparatus (scanner) for reading images on sheets of subject copies, uses an automatic sheet feeding apparatus which separates a plurality of sheet stacked in a stack holding unit and feeding the sheets one by one. In such an automatic sheet feeding apparatus, there is a possibility that separation of the sheets fails and overlap feeding occurs, that is, two or more sheets are fed together in an overlapped manner. Various measures are taken to prevent such overlap feeding.
Typical examples of automatic sheet feeding apparatus having an overlap feeding prevention mechanism include a retard roller system which forcibly turns separating rollers via a torque limiter in a direction reverse to the sheet feeding direction and a return lever system having a return lever, which is operated every time a prescribed number of sheets have been fed to return the leading edges of sheets to a prescribed position. Mechanisms using a return lever include an invention disclosed in U.S. Pat. No. 5,997,198 for instance, a bidirectional rotation control type in which a drive unit of the automatic sheet feeding apparatus is turned in the forward direction to feed sheets and the drive unit is turned in the reverse direction to operate the return lever and thereby return the sheets to a prescribed position. Another is an invention disclosed in Japanese Patent Application Laid-Open No. 2003-54779, a unidirectional rotation control type in which the drive unit of the automatic sheet feeding apparatus is used for rotation only in one direction.
FIG. 9 is a side view of one example of conventional automatic sheet feeding apparatus disclosed in U.S. Pat. No. 5,997,198, and FIG. 10 is a side view of another example of conventional automatic-sheet feeding apparatus disclosed in Japanese Patent Application Laid-Open No. 2003-54779. In the bidirectional rotation control type automatic sheet feeding apparatus disclosed in U.S. Pat. No. 5,997,198, as shown in FIG. 9, a return lever 180 and feed roller conveyance faces 121 are so positioned as to overlap each other, in order to prevent a plurality of sheets, when they are set in a stack holding unit (at the time of sheet setting), from rushing into the sheet feeding apparatus. Or in the unidirectional rotation control type automatic sheet feeding apparatus disclosed in Japanese Patent Application Laid-Open No. 2003-54779, as shown in FIG. 10, a return lever 11 and a lock lever 21 are so positioned as to overlap each other in order to prevent sheets from rushing into the sheet feeding apparatus at the time of sheet setting.
However, working the mechanism to prevent sheets from rushing at the time of sheet setting in either example of the prior art described above is subject to a number of constraints. For instance, the arrangement of so positioning the return lever and the feed roller conveyance faces as to overlap each other involves an inconvenience that the drive configuration and the control thereof are made complex when driving in the direction reverse to sheet conveyance is to be used. Further, this arrangement of so positioning the return lever and the feed roller conveyance faces as to overlap each other involves another inconvenience that, when driving in the sheet conveying direction is to be used, the circumference of the feed roller cannot be effectively used long enough as sheet conveyance faces, with the consequence that the feed means tends to become large. Moreover, if sheets are carelessly inserted when they are to be set in the sheet stack holding unit, the sheets may rush into the sheet feeding apparatus, resulting in a problem in the handling facility of sheet setting. Further in the configuration of so positioning the return lever and the lock lever as to overlap each other, the number of components increase to complicate the mechanism, inviting a larger size or a higher cost.